Low temperature synthesis of nanocrystalline lanthanum monoaluminate powders by chemical coprecipitation

摘要

Nanocrystalline lanthanum monoaluminate (LaAlO_3) powders were prepared by chemical coprecipitation using 25 vol. percent of NH_4OH, 0.05M La(NO_3)_3 centre dot 6H_2O and 0.05 M A1(NO_3)_3 centre dot 9H_2O aqueous solutions as the starting materials. Fourier transform infrared spectroscopy (FT-IR), ther-mogravimetric and differential thermal analyses (TGA/DTA), X-ray diffraction (XRD), Raman spectrometry, specific surface area (BET) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED) were utilized to characterize the LaAlO_3 powders prepared by chemical coprecipitation. The crystallization temperature of the LaAlO_3 precursor gels precipitated at pH 9 is estimated as 810 deg C by TG/DTA. The XRD pattern of the LaAlO_3 precursor gels precipitated at pH 8-12 and calcined at 700 deg C for 6 h shows a broad arciform continuum exist between 24 deg and 32 deg and sharp peaks of LaAlO_3 except the precursor gels precipitated at pH 9. For the LaAlO_3 precursor gels precipitated at pH 9 and calcined at 700 deg C for 6h, the formation of the perovskite LaAlO_3 phase occurs and the presence of crystalline impurities is not found. The crystallite size of LaAlO_3 slightly increases from 37.8 to 41.5 nm with calcination temperature increasing from 700 to 900 deg C for 6h. The LaAlO_3 powders prepared by chemical coprecipitation have a considerably large specific surface of 30 m~2/g. The relative density greater than 97 percent is obtained when these nanocrystalline LaAlO_3 powders are sintered at 1550 deg C for 2 h.